In the use of galvanic cells, particularly alkaline cells, it is not uncommon for the cell to swell and/or leak electrolyte because of improper usage or prolonged storage. For example, if the cell is excessively charged, gas that is normally given off in the charging process can build up in the cell causing the cell to become distorted and if sufficient pressure builds up, the cell can rupture, spilling electrolyte. With high energy cells such as lithium/oxyhalide cells, when operated under certain extreme conditions, there is also the possible danger of cell disassembly and/or fire unless the cells are properly vented.
A cell can be inadvertently subjected to improper usage by the accidental misorientation of the cell in a multicell device. For example, a portable radio, tape player, or flashlight that employs several cells in order to obtain sufficient voltage for the operation of the device can be the site where a cell inadvertently could be added to the electronic device in an incorrect orientation. The cell would then be subjected to charging voltages which could cause it to bulge due to excessive gas pressure and to spill electrolyte in the electronic device. In order to protect the cells from improper charging, diodes have been added which would preclude a reverse potential from being applied to the cell. While a diode does work, it adds unnecessary complexity and expense to the cell. A switch for interrupting the flow of current and isolating the internal components of the galvanic cell is disclosed in U.S. Pat. No. 4,690,879 issued to Huhndorff et al., Sept. 1, 1987, and assigned to the assignee of the present invention. This patent discloses an external electrical contact for the galvanic cell which is adhered to the bottom of the central portion of the cell by a nonconductive adhesive. The perimeter of the contact is welded to the bottom of the cell. On expansion of the cell due to improper use, the bulging of the bottom of the cell will cause the welds to break, interrupting the flow of current and isolating the electrochemical components of the cell.
Another United States patent assigned to the assignee of the present invention is U.S. Pat. No. 4,,756,983 issued to Tucholski on Jul. 12, 1988. This patent discloses a circuit interrupter having a central portion which is adhered to the center of the bottom of the galvanic cell by a nonconductive adhesive and a surrounding flange portion which is welded to the bottom of the cell. Expansion of the cell beyond a predetermined limit will cause the electrical connection between the central portion and the flange to break, electrically isolating the cell.
Both of the circuit interrupters disclosed in the aforementioned patents have been very useful in protecting galvanic cells. Both of the circuit interrupters are used across the continuous bottom portion of the container for the galvanic cell. Neither one of these circuit interrupters is suitable for use in a galvanic cell construction where both the positive and negative external terminals are exposed at the same end of the cell or in a situation where a filling port is provided on the bottom of the cell for adding electrolyte to the galvanic cell, the port then being closed with a suitable fill plug after the cell is full.